1. Field of the Invention
This invention relates to polysiloxanes containing amino groups as additives for improving levelling and wetting in polyurethane-based coatings for plastics.
2. Description of the Prior Art
Plastics, particularly thermoplasts, are being employed to an increasing extent in the automotive industry where they are used, for example, for the production of fenders, spoilers, as linings for exterior parts or the production of other body parts.
It is standard practice to provide these plastic components with a coating for reasons of design or protection. In this connection, it has been found that the wettability of the plastics with the one-component and two-component polyurethane lacquers (coatings) normally used is very limited. This is a particular disadvantage in the case of a multiple-coat lacquer finish wherein the first coat is a base coat based on a physically drying or chemically crosslinking polyurethane binder. The poor wetting of the plastics surface with the base coat, which in general is only very thinly applied, ultimately results in lacquer defects, such as for example pinholes or uneven, poorly levelled surfaces. These defects are attributable to the fact that the individual lacquer droplets of the base coat do not blend with one another on account of the poor wetting. In addition, there is a danger that areas of the substrate which have not been wetted with the base coat may come into contact with the surface coat with the result that the plastic substrate is attacked by strong solvents present in the surface coat.
It has now surprisingly been found that polysiloxanes containing amino groups are suitable as additives in coatings for plastics in order to eliminate the problems mentioned above in regard to wetting and levelling.